Accuracy of Local Polarization Measurements by Scanning Transmission Electron Microscopy

Insights into Chemical and Structural Order at Planar Defects in Pb2MgWO6 Using Multislice Electron Ptychography

Switchable order parameters in ferroic materials are essential for functional electronic devices, yet disruptions of the ordering can take the form of planar boundaries or defects that exhibit distinct properties from the bulk, such as electrical (polar) or magnetic (spin) response. Characterizing the structure of these boundaries is challenging due to their confined size and three-dimensional (3D) nature. Here, a chemical antiphase boundary in the highly ordered double perovskite Pb2MgWO6 is investigated using multislice electron ptychography. The boundary is revealed to be inclined along the electron beam direction with a finite width of chemical intermixing. Additionally, regions at and near the boundary exhibit antiferroelectric-like displacements, contrasting with the predominantly paraelectric matrix. Spatial statistics and density functional theory (DFT) calculations further indicate that despite their higher energy, chemical antiphase boundaries (APBs) form due to kinetic constraints during growth, with extended antiferroelectric-like distortions induced by the chemically frustrated environment in the proximity of the boundary. The three-dimensional imaging reveals the interplay between local chemistry and the polar environment, elucidating the role of antiphase boundaries and their associated confined structural distortions and offering opportunities for engineering ferroic thin films.

Mapping Ferroelectric Fields Reveals the Origins of the Coercivity Distribution

Better techniques for imaging ferroelectric polarization would aid the development of new ferroelectrics and the refinement of old ones. Here we show how scanning transmission electron microscope (STEM) electron beam-induced current (EBIC) imaging reveals ferroelectric polarization with obvious, simply interpretable contrast. Planar imaging of an entire ferroelectric hafnium zirconium oxide (Hf0.5Zr0.5O2, HZO) capacitor shows an EBIC response that is linearly related to the polarization determined in situ with the positive-up, negative-down (PUND) method. The contrast is easily calibrated in MV/cm. The underlying mechanism is magnification-independent, operating equally well on micrometer-sized devices and individual nanoscale domains. Coercive-field mapping reveals that individual domains are biased "positive" and "negative", as opposed to being "easy" and "hard" to switch. The remanent background E-fields generating this bias can be isolated and mapped. Coupled with STEM's native capabilities for structural identification, STEM EBIC imaging provides a revolutionary tool for characterizing ferroelectric materials and devices.

Atomic-scale polarization switching in wurtzite ferroelectrics

Ferroelectric wurtzites have the potential to revolutionize modern microelectronics because they are easily integrated with multiple mainstream semiconductor platforms. However, the electric fields required to reverse their polarization direction and unlock electronic and optical functions need substantial reduction for operational compatibility with complementary metal-oxide semiconductor (CMOS) electronics. To understand this process, we observed and quantified real-time polarization switching of a representative ferroelectric wurtzite (Al_0.94B_0.06N) at the atomic scale with scanning transmission electron microscopy. The analysis revealed a polarization reversal model in which puckered aluminum/boron nitride rings in the wurtzite basal planes gradually flatten and adopt a transient nonpolar geometry. Independent first-principles simulations reveal the details and energetics of the reversal process through an antipolar phase. This model and local mechanistic understanding are a critical initial step for property engineering efforts in this emerging material class.